Electroplating apparatus with electrolyte agitation

ABSTRACT

Electroplating apparatus agitates electrolyte to provide high velocity fluid flows at the surface of a wafer. The apparatus includes a paddle which provides uniform high mass transfer over the entire wafer, even with a relatively large gap between the paddle and the wafer. Consequently, the processor may have an electric field shield positioned between the paddle and the wafer for effective shielding at the edges of the wafer. The influence of the paddle on the electric field across the wafer is reduced as the paddle is spaced relatively farther from the wafer.

TECHNICAL FIELD

The field of the invention is apparatus and methods for agitating liquidelectrolyte in an electroplating apparatus.

BACKGROUND OF THE INVENTION

In many plating processes, a diffusion layer forms in the liquidelectrolyte at the surface of the wafer. The diffusion layer reduces themass transfer rate of electrolyte components and reactants to thesurface of the wafer, which degrades the quality and efficiency of theplating process. One technique for increasing the mass transfer rate isto increase the relative velocity between the liquid electrolyte and thesurface of the workpiece. In the past, some processing apparatus haveused a paddle which oscillates horizontally or vertically in theelectrolyte. The paddle has spaced apart ribs or blades. As the paddlemoves, a liquid vortex is formed in the spaces between adjacent ribs.The liquid vortex creates a high speed agitated flow at or against thelower (down-facing) surface of the workpiece, increasing the masstransfer rate.

These types of paddle plating apparatus also often have an electricfield shield provided to shield the edges of the wafer from the fullelectric field in the electrolyte, to achieve more uniform plating atthe edges of the wafer. The shield is usually an annular ring ofdi-electric material.

Both the paddle and the shield are most effective when positioned veryclose to the wafer, for example, within 5 mm. If the shield ispositioned below the paddle, the shield is less effective. If the shieldis positioned above the paddle, then the paddle is less effective, asthe gap between the paddle and the wafer is larger. Accordingly,engineering challenges remain in designing electro-plating apparatus.

SUMMARY OF THE INVENTION

Experimental and computation results disclose a relationship between thedimension of the gap between the paddle and the wafer, and the vortexsize for achieving improved mass transfer. Specifically, the inventorshave discovered that in processor designs having a larger gap, using apaddle which creates larger vortices provides improved results.Consequently, in designs having a shield is at a vertical position abovethe paddle, making the gap larger, a paddle having ribs spaced fartherapart provides better mass transfer by creating larger vortices. Thevortices may also be made more consistently across the wafer providingmore uniform mass-transfer.

In one aspect, an electroplating apparatus agitates electrolyte toprovide high velocity fluid flow at the surface of a wafer that resultsin results in high, uniform mass transfer providing more uniform platingat high plating rates. The apparatus includes a paddle which can provideuniform high mass transfer over the entire wafer, even with a relativelylarge gap between the paddle and the wafer. Consequently, the processormay have an electric field shield positioned between the paddle and thewafer, where the shield is more effective. In this design, with thepaddle below the shield, the paddle is also less likely to adverselyinfluence the electric field across the wafer. This advantage isparticularly significant in processing where the wafer does not rotate,where such disturbances cannot be averaged out with wafer rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, the same reference number indicates the same element ineach of the views.

FIG. 1 is a top perspective view of an electroplating apparatus.

FIG. 2 is a top perspective view of the apparatus of FIG. 1 with thehead removed for purpose of illustration.

FIG. 3 is a section view of the apparatus of FIG. 1.

FIG. 4 is a top perspective view of the paddle shown in the apparatus ofFIGS. 1-3.

FIG. 5 is a schematic section view of the paddle shown in FIGS. 1-3.

FIG. 6 is a schematic section view of a prior art paddle.

DETAILED DESCRIPTION

As shown in FIGS. 1-3, a processor 10 for electroplating a wafer 30includes a head 14 supported on a head lifter 16 and a vessel 24. Amembrane 40 may be included to divide the vessel 24 into a lower chamber44 containing one or more anodes 28, and a first liquid electrolyte,below the membrane 40, and an upper chamber 42 containing a secondliquid electrolyte. Alternatively the membrane 40 may be omitted withthe vessel 24 having a single chamber holding a single electrolyte.Referring to FIG. 3, a field shaping element 46 made of a dielectricmaterial may be provided in the vessel 24 primarily to support themembrane 40, and distribute flow of catholyte. The electric field in thevessel 24 may be shaped via an anode shield 45, a chamber shield 47, anda weir shield 34. The shields may be annular dielectric elements. Theshields provide shielding of the electric field with the vessel.

A contact ring 26 on the head 14 holds the wafer 30 and has a pluralityof contact fingers for making electrical contact with a conductivelayer, such as a metal seed layer, on the wafer 30. The contact ring 26may optionally have a seal 38 to seal the contact fingers from theelectrolyte. The head 14 may include a rotor 36 for rotating the wafer30 during processing, with the contact ring 26 on the rotor. Typicallythe contact ring has a seal and a backing plate, with the contact ringand the backing plate forming a wafer holder. The head 14 is movable toposition the wafer holder into a processing position in the vessel,where the seed layer is in contact with electrolyte in the vessel.

Referring now also to FIG. 4, a paddle 18 is at a fixed verticalposition within the vessel 24 adjacent to the wafer 30. The paddle 18may be a generally circular plate of dielectric material having aplurality of parallel ribs or blades 60 spaced apart by slots 62. Apaddle actuator 32 moves the paddle 18 horizontally in a flat plane,parallel to the wafer, within the vessel 24 to agitate the electrolyte50. The paddle 18 and the paddle actuator 32 may be supported on a baseplate 20 attached to the vessel 24.

As shown in FIG. 5, a weir shield 34 is provided in the vessel 24between the paddle 18 and the seal 38 of the contact ring 26.Positioning the weir shield 34 above the paddle requires the gap GGbetween the top surface of the ribs 60 of the paddle 18 and the wafer30, to be larger than if the weir shield 34 is positioned below thepaddle 18. Generally, as the gap GG increases, the agitation on thewafer due to the paddle is reduced, which reduces the mass transfer rateand uniformity and the quality of the plating process.

With a seal 38 height of 2-3 mm (2.7 mm nominal), and allowing for a 1mm gap SG between the seal 38 and the weir shield 34, a weir shield 34thickness of 1 mm, and a gap BG of 1 mm between the top of the ribs andthe weir shield 34, the minimum gap GG is about 5-6 mm (5.7 mm nominal).

To achieve a smaller gap GG over most of the wafer 30, a raised ribpaddle 15 as shown in FIG. 6 has been used, with the raised rib paddle15 having taller ribs 60 a over the interior portion of the paddle,where ribs are not at risk of hitting the weir shield 34. Shorter ribs60 b are used at the front and back of the paddle 15 (in the directionMM of paddle movement). The shorter ribs 60B on a first side of thepaddle can move under the weir shield 34 at the limit of paddle travelin a first direction, to a position where the weir shield overlies oneor more of the ribs, and the ribs do not collide with the weir shield34. As the paddle moves to the limit of paddle travel in the opposite orsecond direction, the shorter ribs 60B on the first side of the paddlemove out from under the weir shield, so that the weir shield then doesnot overlie the shorter ribs 60B. With a raised rib paddle 15, the gapGG over much of the wafer can be reduced to about 3-4 mm or less (3.7 mmnominal), rather than 5.7 mm. However, test results using the raised ribpaddle 15 show a thinner plated film at the edges of the wafer, and thatthis results due to the shorter ribs 60 b, which provide reduced masstransfer relative to the taller ribs 60 c.

Referring once again to FIG. 5, with the paddle 18, plating issubstantially uniform, including at the wafer edges. All of the ribs 60on the paddle 18 may have the same height HH. Although the minimum gapGG is 5-6 mm, the paddle 18 achieves plating uniformity better than theraised rib paddle 15. The paddle 18 creates larger vortices, whichmaintains a high level of mass transfer. The ribs 60 are spaced muchfurther apart in comparison to existing designs. For example, in FIG. 5the ribs 60 may be equally spaced apart on at a pitch dimension PP(between centers of adjacent ribs) of 18-22 mm (20.6 mm nominal), with arib height HH equal to 8-13 mm (10.5 mm nominal). As the paddle moves oroscillates in the vessel, the large space 68 between ribs 60 creates alarge diameter vortex which reduces the diffusion layer at the wafersurface and improves mass transfer.

All of the ribs 60 may have the same cross section shape, dimensions andspacing, with the length of the ribs varying with rib position, as shownin FIG. 4. Referring back to FIG. 5, each rib 60 has an upright section64 joined perpendicularly to a base 66 via radii. The radii may beomitted with straight ribs joined perpendicularly to a flat base. Theslots or openings 62 between adjacent bases 66 have a width SS of 4-6 mm(5 mm nominal). Each base 66 has a width BW of 14-17 mm (15.6 mmnominal), and a base height or floor thickness BB of 1-2 mm. The uprightsection 64 may also have a width or thickness of 1-2 mm and a pluralityof equally spaced apart upright ribs.

The inventors have discovered that there is a mathematical relationshipbetween the gap GG and the pitch spacing PP (or alternatively the widthof the space 68 formed between adjacent ribs).

1. PP=2.72×GG+3.45 mm.

2. Space aspect ratio=(HH−BB)/PP=0.3 to 0.5 (0.44 nominal).

Consequently, in processor design, the gap GG may be first determinedbased on the shield requirements and other factors. Then the paddle 18may be designed with the pitch and height of the ribs selected to havean aspect ratio of 0.3 or 0.35 to 0.5, and PP is greater than 16, 17 or18 mm, and up to 22 or 24 mm. Using these equations, the thickness BB ofthe base 66 is added to obtain the total rib height HH. Although the gapGG varies depending on dimensions of other elements and the design ofthe electroplating processor, the ratio of PP/GG may typically rangefrom about 2.5 to 3.

Thus, a novel electroplating processor has been shown and described.Various changes and substitutions may of course be made withoutdeparting from the spirit and scope of the invention. The invention,therefore, should not be limited, except by the following claims, andtheir equivalents.

1. An electroplating processor, comprising: a vessel; a head having awafer holder, with the head movable to position the wafer holder in thevessel; a contact ring on the head having a plurality of electricalcontacts positioned for making electrical contact with a wafer held bythe wafer holder; at least one anode in the vessel; a paddle in thevessel, with the paddle having a plurality of equally spaced 1.0 apartupright ribs, with substantially all of the ribs having a height HH, andwith the ribs having a pitch spacing PP greater than 16 mm, and withratio of HH:PP equal to 0.35 to 0.5; and a paddle actuator attached tothe paddle for moving the paddle horizontally within the vessel.
 2. Theelectroplating processor of claim 1 with the wafer holder holding awafer at a processing position, with a gap of 4-6 mm between a lowersurface of the wafer and a top surface of the ribs.
 3. Theelectroplating processor of claim 1 with each rib joined to a base, andwith an opening of 4-6 mm between bases of adjacent ribs.
 4. Theelectroplating processor of claim 3 with each base having a width BW andwith BW equal to 70 to 95% of HH.
 5. The electroplating processor ofclaim 1 with PP equal to 18 to 22 mm.
 6. The electroplating processor ofclaim 1 further including a seal on the contact ring, and with the sealand the weir shield at a vertical level above the ribs.
 7. Theelectroplating processor of claim 6 with the paddle actuator moving thepaddle from a first position, wherein the weir shield overlies the firstrib, to a second position wherein the weir shield does not overlie thefirst rib.
 8. The electroplating processor of claim 1 wherein the paddleis round and comprises a di-electric material, and substantially all ofthe ribs are equally spaced apart.
 9. The electroplating processor ofclaim 5 with HH:PP equal to 0.4 to 0.5.
 10. An electroplating processor,comprising: a vessel for holding a liquid electrolyte; a head having awafer holder; a head lifter attached to the head, with the head liftermovable to position the wafer holder in the vessel; a contact ring onthe head having a plurality of electrical contacts positioned for makingelectrical contact with a wafer held by the wafer holder; a seal on thecontact ring; at least one anode in the vessel; a circular di-electricmaterial paddle at a fixed vertical position in the vessel, with thepaddle having a plurality of equally spaced apart upright ribs, withsubstantially all of the ribs having a height HH, and with the ribshaving a pitch spacing PP, and with ratio of HH:PP equal to 0.35 to 0.5;and a paddle actuator attached to the paddle for moving the paddlehorizontally within the vessel.
 11. The electroplating processor ofclaim 10 with the wafer holder holding a wafer at a processing position,with a gap of 4-6 mm between a lower surface of the wafer and topsurfaces of the ribs.
 12. The electroplating processor of claim 10 witheach rib has an upright vertical section joined perpendicularly to ahorizontal base.
 13. The electroplating processor of claim 12 with anopening of 4-6 mm between bases of adjacent ribs.
 14. The electroplatingprocessor of claim 12 with each base having a width BW and with BW equalto 65 to 100% of HH.
 15. The electroplating processor of claim 14 withPP equal to 18 to 22 mm.
 16. The electroplating processor of claim 10with the paddle actuator moving the paddle from a first position,wherein the weir shield and the seal overlie the first rib, to a secondposition wherein the weir shield and the seal do not overlie the firstrib.
 17. The electroplating processor of claim 10 further including aweir shield in the vessel above the paddle.
 18. The electroplatingprocessor of claim 1 further including a weir shield in the vessel abovethe paddle.
 19. An electroplating processor, comprising: a vessel; ahead having a wafer holder, with the head movable to position the waferholder in the vessel; a contact ring on the head having a plurality ofelectrical contacts positioned for making electrical contact with awafer held by the wafer holder; at least one anode in the vessel; apaddle in the vessel, with the paddle having a plurality of equallyspaced apart upright ribs, with substantially all of the ribs having aheight HH, and with the ribs having a pitch spacing PP greater than 18mm, and with ratio of HH:PP equal to 0.35 to 0.5; a paddle actuatorattached to the paddle for moving the paddle horizontally within thevessel; and a weir shield in the vessel above the paddle.